Disclosed herein is a clear toner composition particular suitable for overcoating applications. Also disclosed herein is an image forming process using the clear toner composition.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrophotographic imaging process, as taught by C. F. Carlson in U.S. Pat. No. 2,297,691, entails placing a uniform electrostatic charge on a photoconductive insulating layer known as a photoconductor or photoreceptor, exposing the photoreceptor to a light and shadow image to dissipate the charge on the areas of the photoreceptor exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material known as toner. Toner typically comprises a resin and a colorant. The toner will normally be attracted to those areas of the photoreceptor which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This developed image may then be transferred to a substrate such as paper. The transferred image may subsequently be permanently affixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
Numerous processes are within the purview of those skilled in the art for the preparation of toners. Emulsion aggregation (EA) is one such method. Emulsion aggregation toners can be used in forming print and/or xerographic images. Emulsion aggregation techniques can entail the formation of an emulsion latex of the resin particles by heating the resin, using emulsion polymerization, as disclosed in, for example, U.S. Pat. No. 5,853,943, the disclosure of which is totally incorporated herein by reference.
Exemplary emulsion aggregation toners include acrylate based toners, such as those based on styrene acrylate toner particles as illustrated in, for example, U.S. Pat. No. 6,120,967, the disclosure of which is totally incorporated herein by reference.
In some printing processes, a final step is employed in which a clear overcoat is applied to the print for various reasons, such as protection of the print, gloss improvement and uniformity, or the like. Various means exist for applying this overcoat, including the use of a clear toner. While known compositions and processes are suitable for their intended purposes, a need remains for improved clear overcoat toners. In addition, a need remains for overcoat toners that exhibit high gloss. Further, a need remains for overcoat toners that exhibit improved release from the fuser roll. Additionally, a need remains for overcoat toners that exhibit relatively low haze. There is also a need for overcoat toners that exhibit a high degree of transparency. There is also a need for overcoat toners with desirable flow characteristics that enable improved flow on the page that does not penetrate into the cellulose fibers and lose gloss and contributing to an even layer of toner on the page preventing irregularities in the coating. In addition, there is a need for overcoat toners that exhibit low blocking. Further, there is a need for overcoat toners that exhibit good print performance. Additionally, there is a need for overcoat toners that exhibit good flow, particle size, particle shape, and distribution of coarse and fine particles. A need also remains for overcoat toners that exhibit high gloss and transparency, enabling better photograph-like image quality.